posted on 2012-03-30, 12:29authored byVincent Stanley Williams
Understanding the feeding mechanisms and diet of ornithopod dinosaurs is
fundamental to understanding their role in Late Cretaceous ecosystems. Current
hypotheses of feeding behaviour are based on functional morphology, and testing these
is problematic. Microscopic scratches, microwear, that form on teeth in vivo during
feeding are known to record the relative movement of the tooth rows and to capture
evidence of tooth-food interactions; however, their applicability to ornithischian
dinosaurs has not been tested. The development of a fast non-abrasive and residue free
method for the removal of resistant consolidant, along with a safe, rapid technique for
replicating tooth surfaces was the first step towards assessing the suitability of
quantitative tooth microwear analysis techniques for dinosaur teeth. An evaluation of
appropriate statistical analysis methods followed, identifying suitably stringent tests for
the analysis of variance in the multi-modal directional microwear data. Analysis of
microwear orientation in Iguana iguana provided direct evidence for relative motion of
the jaws. Microwear from the basal ornithischian Lesothosaurus diagnosticus revealed
three distinct sets of scratches in different orientations that were comparable to those of
I. iguana, confirming the isognathic, near-vertical, simple adduction predicted for this
dinosaur. Results from the basal ornithopod Hypsilophodon foxii indicate a propalinal
translation of the lower jaw during feeding and provide strong support for muscular
cheeks, whilst those from the hadrosaurid Edmontosaurus indicate a near-vertical
posterodorsal power stroke with a secondary propalinal action and support the presence
of a pleurokinetic hinge. Analysis of a range of hadrosaurid taxa found that three
differing mastication methods existed, potentially diet related. Furthermore, microwear
suggests that here is no significant difference in the jaw mechanics between
iguanodontians and hadrosaurids. The results demonstrate that microwear has great
potential for unravelling the mystery of dinosaur feeding and identifying key stages in
the evolution of jaw mechanics in ornithopods.